This project investigates the use of vocal signals by squirrel monkeys in specified contexts as a model language. Three main areas of research were pursued during the reporting period. 1) Affiliative vocalizations continued to be a major focus, with new findings being reported on the temporal patterning of vocal exchanges between individual females sharing affiliative relationships. 2) A major study of play behavior in a group of 10 yearling monkeys was completed, with these results: Youngsters show both sex and individual differences in the frequency and roughness of their play. Females and subordinate males avoid partners which would overpower them in wrestling play, or they initiate play of a milder type with these partners. The tendency of dominant individuals to take on a subordinate role in play (role reversal) encourages play between youngsters of differing abilities or size. These strategies foster play within a group and enable immature monkeys to miximize play experiences which promote normal social and behavioral development. Vocal correlates of play are still being analyzed. 3) Information content in contact and alarm calls has been studied utilizing playback methodology. This work involves presenting tape recorded sounds to multi-age, multi-sex groups of monkeys, and has been made possible by construction of new outdoor habitats. A significant finding demonstrates that mothers can recognize their own infants on the basis of a particular class of contact call - the isolation call. Early results with alarm calls suggests some individuality there as well and raises the possibility that listeners may respond differentially to alarm calls from near relatives.